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' Performa Inc. • • May 7,2003 Page 10 ' ground water to the extent that the nitrate-nitrogen concentration of ground-water flow from up- gradient areas is lower." ' Hantzsche and Fennemore indicate that the approach to predicting nitrate buildup in ground water is"...a conservative(worst case) first approximation of ground-water nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and precipitation. This (the equation and approach)is for estimation of long-term effect(i.e., over years) on ground-water quality, and is not intended for prediction of seasonal changes." The method takes into account development area, soil denitrification factor, rainfall volume, rainfall nitrate concentration, the waste effluent quantity, and waste effluent nitrate concentration. The formula, assumptions and calculations used for the analysis are shown on Plates 4 through 6. The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water contaminate level is 10 mg/L. These variables are discussed next. 6.2 Quantity and Quality of Septic System Effluent We understand that the numbers both of office employees and of visiting truck drivers will be greatly increasing with the proposed expansion of the facility. Office workers are expected to total 23, each working an eight-hour shift Monday through Friday. Mechanics will total 15,with five mechanics working each of three, eight-hour shifts, seven days a week. We understand that the number of truck drivers passing through the site should be calculated ' based on the following observations made at similar Schneider facilities: • Drivers take 2.5 showers per hour per shower during peak use times • Peak hours are 6 a.m. to 10 p.m., 16 hours total • Only half the drivers visiting a facility take a shower • Four showers total will exist at the facility after expansion 80 drivers may pass through the site during non-peak hours each day Weekend traffic of drivers is approximately 70%of weekday traffic • The average driver spends 1-2 hours at the facility but may spend up to 4 hours if truck maintenance is performed We employed the following calculation to determine the potential number of drivers visiting the site each day: ' (2.5 showers/peak hour/shower)(16 peak hours)(2*)(4 showers)=320 peak hours weekday drivers 320 peak hours weekday drivers+80 non-peak hours weekday drivers=400 weekday drivers 400 weekday drivers x 70%=280 weekend drivers *because only half the drivers use the showers B's ,